Image sensor including control electrode, transparent electrode, and connection layer electrically connecting control electrode to side surface of transparent electrode

ABSTRACT

An image sensor includes pixel electrodes, a control electrode, a photoelectric conversion film arranged on the pixel electrodes, a transparent electrode arranged on the photoelectric conversion film, an insulating layer arranged on at least a portion of a top surface of the transparent electrode, and a connection layer that electrically connects the control electrode to the transparent electrode. The connection layer is in contact with at least one side surface of the transparent electrode. A side surface of the insulating layer, the at least one side surface of the transparent electrode, and a side surface of the photoelectric conversion film are aligned with each other.

BACKGROUND 1. Technical Field

The present disclosure relates to an image sensor and a fabricationmethod therefor.

2. Description of the Related Art

An image sensor includes a photo-detecting element that generates anelectrical signal in relation to the amount of incident light andincludes a plurality of pixels arranged in one dimension or twodimensions. A multilayer image sensor refers to, among image sensors, animage sensor having, as a pixel, a photo-detecting element having astructure in which a pixel electrode, a photoelectric conversion film,and a transparent electrode are stacked in order from the substrateside.

The photo-detecting element of the multilayer image sensor is connectedto a signal detection circuit via the pixel electrode and connected to avoltage control element via the transparent electrode. The signaldetection circuit detects an electrical signal generated by incidentlight on the photo-detecting element.

The voltage control element performs control such that the voltage ofthe transparent electrode falls within a specified range so that thesignal detection circuit can properly detect the electrical signalgenerated in the photo-detecting element. In a case where an electriccurrent flows from the pixel electrode, the voltage control elementcauses an electric current as much as the electric current to flowthrough the transparent electrode, so that the photo-detecting elementis prevented from being charged.

Japanese Unexamined Patent Application Publication No. 2014-60315 andU.S. Pat. No. 9,224,789 disclose an image sensor including aphotoelectric conversion film formed of an organic semiconductor, atransparent electrode formed on the organic photoelectric conversionfilm, a protective film formed on the transparent electrode, and awiring line that electrically connects the transparent electrode exposedin an opening provided in the protective film to the voltage controlelement.

SUMMARY

In one general aspect, the techniques disclosed here feature anexemplary image sensor according to the present disclosure includingpixel electrodes, a control electrode, a photoelectric conversion filmarranged on the pixel electrodes, a transparent electrode arranged onthe photoelectric conversion film, an insulating layer arranged on atleast a portion of a top surface of the transparent electrode, and aconnection layer that electrically connects the control electrode to thetransparent electrode. The connection layer is in contact with at leastone side surface of the transparent electrode. A side surface of theinsulating layer, the at least one side surface of the transparentelectrode, and a side surface of the photoelectric conversion film arealigned with each other.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a circuit configuration of animaging device;

FIG. 2 is a schematic diagram illustrating a cross section of a devicestructure of a unit pixel cell in the imaging device;

FIG. 3A is a schematic cross section of an image sensor of a presentembodiment;

FIG. 3B is a schematic top view of the image sensor of the presentembodiment with its protective film removed;

FIG. 4A is a cross section illustrating a step in an image sensorfabrication method of the present embodiment;

FIG. 4B is a cross section illustrating steps in the image sensorfabrication method of the present embodiment;

FIG. 4C is a cross section illustrating a step in the image sensorfabrication method of the present embodiment;

FIG. 4D is a cross section illustrating the step in the image sensorfabrication method of the present embodiment;

FIG. 4E is a cross section illustrating the step in the image sensorfabrication method of the present embodiment;

FIG. 4F is a cross section illustrating a step in the image sensorfabrication method of the present embodiment;

FIG. 4G is a cross section illustrating the step in the image sensorfabrication method of the present embodiment;

FIG. 4H is a cross section illustrating a step in the image sensorfabrication method of the present embodiment;

FIG. 5 is a schematic cross section illustrating a portion of anotherform of the image sensor;

FIG. 6 is a schematic top view of the other form of the image sensorwith its protective film removed;

FIG. 7 is a schematic top view of another form of the image sensor withits protective film removed;

FIG. 8 is a schematic top view of another form of the image sensor withits protective film removed;

FIG. 9A is a top view of another form of the image sensor;

FIG. 9B is a schematic cross section illustrating a portion of the otherform of the image sensor of FIG. 9A; and

FIG. 10 is a cross section illustrating a step in another form of theimage sensor fabrication method.

DETAILED DESCRIPTION

In a multilayer image sensor, the sensitivity of a photoelectricconversion film formed of a certain kind of material greatly changesdepending on the voltage applied to the transparent electrode, and thesensitivity can be made virtually zero. By using this characteristic, amultilayer image sensor capable of performing electronic shutteroperation can be realized by changing the voltage of the transparentelectrode.

Furthermore, for another photoelectric conversion film, the opticalspectrum, which is a spectral sensitivity characteristic, of thephotoelectric conversion film can be greatly changed depending on thevoltage applied to the transparent electrode. By using thischaracteristic, in a multilayer image sensor of a certain type, thespectral sensitivity characteristic of the photoelectric conversion filmcan be changed among two or more different spectral sensitivitycharacteristics by changing the voltage of the transparent electrode.

For these image sensors, a voltage control element realizes a functionfor operating an electronic shutter or a function for changing thespectral sensitivity characteristic by temporally changing the voltageapplied to the transparent electrode.

In this manner, in a multilayer image sensor, in order that the signaldetection circuit properly detects an electrical signal generated in thephoto-detecting element, the voltage control element needs to performcontrol such that the voltage of the transparent electrode falls withina specified range. In addition, in a case where an electric currentflows from a pixel electrode, an electric current needs to flow betweenthe voltage control element and the transparent electrode so that thephoto-detecting element is prevented from being charged.

For these types of control or operation, the lower the resistance of avoltage application path including the transparent electrode between thevoltage control element and the photoelectric conversion film, thesmaller the voltage change and power consumption, and the higher thespeed of temporal change, which are examples of advantages.

In contrast, some materials used in the photoelectric conversion filmreact with, for example, oxygen, ozone, or moisture, so that thephotoelectric conversion function deteriorates. For example, in a casewhere the photoelectric conversion film is formed of an organicsemiconductor, the organic semiconductor contains a material that tendsto react with, for example, oxygen, ozone, or moisture. Thus, during thefabrication process of an image sensor, preferably, the photoelectricconversion film is formed and patterned in an environment in which thephotoelectric conversion function does not deteriorate. For example,preferably, the photoelectric conversion film is formed and patternedunder an inert atmosphere of, for example, nitrogen or a vacuum.

However, generally, a significantly large-scale fabrication apparatus isneeded to perform the entirety of the formation and patterning of thephotoelectric conversion film under an inert atmosphere or a vacuum. Inaddition, also in a case where a wafer on which the photoelectricconversion film is formed is conveyed between fabrication apparatuses,large-scale conveying equipment is needed to perform such conveyanceunder an inert atmosphere.

The inventors of the present disclosure conceived image sensors havingnovel structures in which a voltage control element is connected to aphotoelectric conversion film with low resistance and with which thephotoelectric conversion film can be easily handled during thefabrication process. The summary of image sensors and image sensorfabrication methods of the present disclosure is as follows.

[Item 1]

An image sensor according to Item 1 of the present disclosure includespixel electrodes,a control electrode,a photoelectric conversion film arranged on the pixel electrodes,a transparent electrode arranged on the photoelectric conversion film,an insulating layer arranged on at least a portion of a top surface ofthe transparent electrode, anda connection layer that electrically connects the control electrode tothe transparent electrode.

The connection layer is in contact with at least one side surface of thetransparent electrode, and

a side surface of the insulating layer, the at least one side surface ofthe transparent electrode, and a side surface of the photoelectricconversion film are aligned with each other.

In this case, the transparent electrode may be formed of a conductivesemiconductor. The control electrode may be formed of a metal or ametallic compound.

[Item 2]

In the image sensor described in Item 1, the connection layer may alsobe in contact with the side surface of the photoelectric conversionfilm.

[Item 3]

In the image sensor described in Item 1 or 2, the connection layer maycover a portion of the insulating layer.

[Item 4]

In the image sensor described in any one of Items 1 to 3, the connectionlayer does not have to be in contact with the top surface of thetransparent electrode.

[Item 5]

In the image sensor described in any one of Items 1 to 4, in plan view,the connection layer may partially overlap with the pixel electrodes.

[Item 6]

In the image sensor described in any one of Items 1 to 5, the connectionlayer may have a light-blocking property.

[Item 7]

The image sensor described in any one of Items 1 to 6 may furtherinclude a protective film that covers the connection layer and theinsulating layer,

[Item 8]

In the image sensor described in any one of Items 1 to 7,in plan view, the transparent electrode may have a polygonal shape,the at least one side surface of the transparent electrode may include aplurality of side surfaces, andthe connection layer may be in contact with the plurality of sidesurfaces of the transparent electrode.

[Item 9]

In the image sensor described in any one of Items 1 to 8,a hole through which the top surface of the transparent electrode isconnected to the connection layer does not have to be arranged in theinsulating layer.

[Item 10]

In the image sensor described in any one of Items 1 to 9,in plan view, the connection layer may overlap with at least a portionof the insulating layer, at least a portion of the transparentelectrode, and at least a portion of the photoelectric conversion film.

[Item 11]

A method for fabricating an image sensor according to Item 11 of thepresent disclosure includespreparing a substrate on which pixel electrodes and a control electrodeare provided,forming a photoelectric conversion film on the pixel electrodes,forming a transparent electrode on a top surface of the photoelectricconversion film,forming an insulating layer on the transparent electrode,patterning the photoelectric conversion film, the transparent electrode,and the insulating layer so that a side surface of the insulating layer,a side surface of the transparent electrode, and a side surface of thephotoelectric conversion film are aligned with each other, andforming a connection layer that electrically connects the side surfaceof the transparent electrode, which is exposed by the patterning, to thecontrol electrode.

[Item 12]

In the method described in Item 11,in the patterning, a hole through which a top surface of the transparentelectrode is connected to the connection layer does not have to beformed in the insulating layer.

[Item 13]

In the method described in Item 11 or 12,in the forming of the connection layer, the connection layer may bebrought into contact with the photoelectric conversion film.

[Item 14]

In the method described in any one of Items 11 to 13,in the patterning, the insulating layer may be patterned so as to exposean outer periphery of a top surface of the transparent electrode, andin the forming of the connection layer, the connection layer may bebrought into contact with the outer periphery of the transparentelectrode.

[Item 15]

In the method described in any one of Items 11 to 14,in the forming of the connection layer, the connection layer may beformed on at least a portion of the insulating layer.

[Item 16]

An image sensor fabrication method according to Item 16 of the presentdisclosure includes a step (A) for preparing a circuit portion that hasa plurality of pixel electrodes and a control electrode,a step (B) for forming a photoelectric conversion film on the pluralityof pixel electrodes,a step (C) for forming a transparent electrode formed of a conductivesemiconductor on a top surface of the photoelectric conversion film,a step (D) for forming an insulating layer on the transparent electrode,a step (E) for performing patterning by removing each of a portion ofthe photoelectric conversion film, a portion of the transparentelectrode, and a portion of the insulating layer, anda step (F) for forming a connection layer that electrically connects aside surface of the transparent electrode exposed by performing the step(E) to the control electrode.

[Item 17]

In the image sensor fabrication method described in Rem 16, in the step(F), the connection layer may also be joined to the photoelectricconversion film.

[Item 18]

In the image sensor fabrication method described in Rem 16,in the step (E),the portion of the transparent electrode and the portion of theinsulating layer may be removed by dry etching using a gas containing atleast one of chlorine andfluorine, andthe portion of the photoelectric conversion film may be removed by dryetching using a gas containing oxygen.

[Item 19]

In the image sensor fabrication method described in any one of Items 16to 18, in the step (E), the insulating layer may be patterned so as toexpose an outer peripheral portion of the top surface of the transparentelectrode, andin the step (F), the connection layer may also be joined to the outerperipheral portion of the transparent electrode.

[Item 20]

In the image sensor fabrication method described in any one of Items 16to 18, in the step (F), the connection layer may be formed on at least aportion of the insulating layer.

Hereinafter, embodiments of image sensors of the present disclosure willbe described with reference to the drawings.

Overview of Imaging Device including Image Sensor

First, an imaging device that uses an image sensor of the presentdisclosure will be described in general terms. FIG. 1 schematicallyillustrates a circuit configuration of an imaging device 500. Theimaging device 500 includes an image sensor 101 including a plurality ofunit pixel cells 14 and a peripheral circuit.

The plurality of unit pixel cells 14 are arranged on a semiconductorsubstrate two-dimensionally, that is, in a row direction and a columndirection to form a pixel region. The image sensor 101 may be a linesensor. In that case, the plurality of unit pixel cells 14 may bearranged in one dimension. Herein, the row direction and the columndirection refer to the direction in which rows extend and the directionin which columns extend, respectively. That is, the vertical directionis the column direction, and the horizontal direction is the rowdirection.

Each unit pixel cell 14 includes a photodetector 10, an amplificationtransistor 11, a reset transistor 12, and an address transistor 13,which is a row selection transistor. The photodetector 10 includes apixel electrode 50 and a transparent electrode 52. The image sensor 101includes a voltage control element for applying a predetermined voltageto the transparent electrode 52. The voltage control element is, forexample, a voltage control circuit, a voltage generation circuit such asa constant voltage source, or a voltage reference line such as a groundwire. The voltage applied by the voltage control element is called acontrol voltage. In the present embodiment, a voltage control circuit 60is provided as the voltage control element. The voltage control circuit60 may generate a constant control voltage or a plurality of controlvoltages having different values from each other. For example, two ormore control voltages having different values from each other may begenerated, or the control voltage that continuously changes in apredetermined range may be generated. The voltage control circuit 60determines the value of a control voltage to be generated, on the basisof a command from an operator who operates the imaging device 500 and acommand from, for example, another control unit included in the imagingdevice 500 and generates a control voltage whose value has beendetermined. The voltage control circuit 60 is provided, as a portion ofthe peripheral circuit, outside a photosensitive area. That is, thevoltage control circuit 60 may be included in the image sensor 101.

For example, the voltage control circuit 60 generates two or moredifferent control voltages, and the spectral sensitivity characteristicof a photoelectric conversion film 51 is changed by applying the controlvoltages to the transparent electrode 52. In addition, the variations inthe spectral sensitivity characteristic include a spectral sensitivitycharacteristic in which the sensitivity of the photoelectric conversionfilm 51 becomes zero with respect to light to be detected. Thus, forexample, while the unit pixel cell 14 is reading out a detection signalon a row-by-row basis in the imaging device 500, the effect of incidentlight when the detection signal is read out can be made virtually zeroby applying, from the voltage control circuit 60 to the transparentelectrode 52, the control voltage with which the sensitivity of thephotoelectric conversion film 51 becomes zero. Therefore, it is possibleto realize a global shutter operation even in a case where the detectionsignal is substantially read out on a row-by-row basis.

In the present embodiment, by applying the control voltage to thetransparent electrodes 52 of the unit pixel cells 14 arranged in the rowdirection via a counter electrode signal line 16 as illustrated in FIG.1, the voltage between the pixel electrode 50 and the transparentelectrode 52 of each unit pixel cell 14 is changed, thereby switchingbetween the spectral sensitivity characteristics in the photodetector10. Alternatively, an electronic shutter operation is realized byapplying the control voltage at a predetermined timing during imaging sothat a spectral sensitivity characteristic in which the sensitivity tolight becomes zero is obtained. The control voltage may be applied tothe pixel electrode 50. In order to irradiate the photodetector 10 withlight and store holes at the pixel electrode 50 as a signal charge, thepixel electrode is set to a relatively low potential with respect to thetransparent electrode 52. In this case, an electric current flows fromthe pixel electrode 50 to the transparent electrode 52 since thedirection in which electrons move is opposite. In addition, in order toirradiate the photodetector 10 with light and accumulate holes at thepixel electrode 50 as a signal charge, the pixel electrode is set to arelatively low potential with respect to the transparent electrode 52.In this case, an electric current flows from the pixel electrode 52 tothe transparent electrode 50.

The pixel electrode 50 is connected to the gate electrode of theamplification transistor 11, and the signal charge collected by thepixel electrode 50 is stored in a charge storage node 24, which ispositioned between the pixel electrode 50 and the gate electrode of theamplification transistor 11. In the present embodiment, the signalcharge is holes; however, the signal charge may be electrons.

The signal charge stored in the charge storage node 24 is applied to thegate electrode of the amplification transistor 11 as a voltage inrelation to the amount of signal charge. The amplification transistor 11is included in a signal detection circuit and amplifies the voltageapplied to the gate electrode. The address transistor 13 selectivelyreads out the amplified voltage as a signal voltage. The source-drainelectrode of the reset transistor 12 is connected to the pixel electrode50 and resets the signal charge stored in the charge storage node 24. Inother words, the reset transistor 12 resets the potential of the gateelectrode of the amplification transistor 11 and that of the pixelelectrode 50.

In order to perform the above-described operation for the plurality ofunit pixel cells 14 in a selective manner, the imaging device 500includes power wiring lines 21, vertical signal lines 17, address signallines 26, and reset signal lines 27, and these lines are connected tocorresponding unit pixel cells 14. Specifically, for each unit pixelcell 14, the power wiring line 21 is connected to the source-drainelectrode of the amplification transistor 11, and the vertical signalline 17 is connected to the source-drain electrode of the addresstransistor 13. The address signal line 26 is connected to the gateelectrode of the address transistor 13. The reset signal line 27 isconnected to the gate electrode of the reset transistor 12.

The peripheral circuit includes a vertical scanning circuit 15, ahorizontal signal readout circuit 20, a plurality of column signalprocessing circuits 19, a plurality of load circuits 18, and a pluralityof differential amplifiers 22, The vertical scanning circuit 15 is alsocalled a row scanning circuit. The horizontal signal readout circuit 20is also called a column scanning circuit. The column signal processingcircuits 19 are also called row signal storage circuits. Thedifferential amplifiers 22 are also called feedback amplifiers.

The vertical scanning circuit 15 is connected to the address signallines 26 and the reset signal lines 27 and selects, on a row-by-rowbasis, a row of unit pixel cells 14 from among the plurality of unitpixel cells 14 arranged in individual rows to read out signal voltagesand reset the potential of the pixel electrodes 50. The power wiringlines 21, which are a source follower power supply, supply apredetermined power supply voltage to each unit pixel cell 14. Thehorizontal signal readout circuit 20 is electrically connected to theplurality of column signal processing circuits 19. Each column signalprocessing circuit 19 is electrically connected to the unit pixel cells14 arranged in a corresponding one of the columns via the verticalsignal line 17 corresponding to the column. The load circuits 18 areelectrically connected to the respective vertical signal lines 17. Eachamplification transistor 11 and its corresponding load circuit 18 form asource follower circuit.

The plurality of differential amplifiers 22 are provided so as tocorrespond to the respective columns. The negative input terminal ofeach differential amplifier 22 is connected to the correspondingvertical signal line 17. Moreover, the output terminal of thedifferential amplifier 22 is connected to the unit pixel cells 14 via afeedback line 23 corresponding to the column.

The vertical scanning circuit 15 applies a row selection signal forcontrolling ON-OFF of the address transistors 13 to the gate electrodesof the address transistors 13 through an address signal line 26.Consequently, the row to be read is scanned and selected. The signalvoltages are read out from the unit pixel cells 14 of the selected rowto the vertical signal lines 17. Moreover, the vertical scanning circuit15 applies a reset signal for controlling ON-OFF of the resettransistors 12 to the gate electrodes of the reset transistors 12through the reset signal line 27. Consequently, the row of unit pixelcells 14 to be reset is selected. The vertical signal lines 17 transmitthe signal voltages read out from the unit pixel cells 14 selected bythe vertical scanning circuit 15 to the column signal processingcircuits 19.

The column signal processing circuits 19 perform noise suppressionsignal processing, notably correlated double sampling, andanalog-to-digital conversion (AD conversion).

The horizontal signal readout circuit 20 reads out the signalssuccessively from the plurality of column signal processing circuits 19to a horizontal common signal line (not illustrated).

The differential amplifier 22 is connected to the drain electrodes ofthe reset transistors 12 via the feedback line 23. Thus, when one of theaddress transistors 13 and the reset transistor 12 are in the conductivestate, the differential amplifier 22 receives, through the negativeterminal, an output value of the address transistor 13. The differentialamplifier 22 performs feedback operation so that the gate potential ofthe amplification transistor 11 becomes a predetermined feedbackvoltage. In this case, the output voltage value of the differentialamplifier 22 is 0 V or a positive voltage near 0 V. The feedback voltagemeans the output voltage of the differential amplifier 22.

FIG. 2 schematically illustrates a cross section of a device structureof the unit pixel cell 14 in the imaging device 500, The unit pixel cell14 includes a semiconductor substrate 31, a charge detection circuit 25,and a photodetector 10. The semiconductor substrate 31 is; for example;a p-type silicon substrate. The charge detection circuit 25 detects asignal charge captured by the pixel electrode 50 and outputs a signalvoltage. The charge detection circuit 25 includes the amplificationtransistor 11, the reset transistor 12, and the address transistor 13and is formed in and on the semiconductor substrate 31.

The amplification transistor 11 includes n-type impurity regions 41C and41D, a gate insulating layer 38B, and a gate electrode 398. The n-typeimpurity regions 41C and 41D are formed in the semiconductor substrate31 and respectively function as the drain electrode and the sourceelectrode. The gate insulating layer 383 is positioned on thesemiconductor substrate 31, and the gate electrode 39B is positioned onthe gate insulating layer 38B.

The reset transistor 12 includes n-type impurity regions 4B and 41A, agate insulating layer 38A, and a gate electrode 39A. The n-type impurityregions 418 and 41A are formed in the semiconductor substrate 31 andrespectively function as the drain electrode and the source electrode.The gate insulating layer 38A is positioned on the semiconductorsubstrate 31, and the gate electrode 39A is positioned on the gateinsulating layer 38A.

The address transistor 13 includes n-type impurity regions 41D and 41E,a gate insulating layer 38C, and a gate electrode 39C. The n-typeimpurity regions 41D and 41E are formed in the semiconductor substrate31 and respectively function as the drain electrode and the sourceelectrode. The gate insulating layer 38C is positioned on thesemiconductor substrate 31, and the gate electrode 39C is positioned onthe gate insulating layer 38C. The n-type impurity region 41D is sharedby the amplification transistor 11 and the address transistor 13, andthus the amplification transistor 11 and the address transistor 13 areconnected in series.

In the semiconductor substrate 31, an element isolation region 42 isprovided between the unit pixel cell 14 and an adjacent unit pixel cell14 and between the amplification transistor 11 and the reset transistor12. The element isolation region 42 electrically separates the adjacentunit pixel cells 14 from each other. In addition, the leakage of signalcharge stored in the charge storage node is suppressed.

Interlayer insulating layers 43A, 43B, and 43C are stacked on thesurface of the semiconductor substrate 31. In the interlayer insulatinglayer 43A, a contact plug 45A, a contact plug 45B, and a wiring line 46Aare embedded. The contact plug 45A is connected to the n-type impurityregion 41B of the reset transistor 12, the contact plug 45B is connectedto the gate electrode 39B of the amplification transistor 11, and thewiring line 46A connects the contact plug 45A to the contact plug 45B.As a result, the n-type impurity region 41B (the drain electrode) of thereset transistor 12 is electrically connected to the gate electrode 393of the amplification transistor 11. Moreover, the wiring line 46A iselectrically connected to the pixel electrode 50 via a contact plug 47A,a wiring line 463, a contact plug 47B, a wiring line 46C, and a contactplug 47C.

The photodetector 10 is provided in and on the interlayer insulatinglayer 43C. The photodetector 10 includes the transparent electrode 52,the photoelectric conversion film 51, and the pixel electrode 50, whichis positioned closer to the semiconductor substrate 31 than thetransparent electrode 52 is. The photoelectric conversion film 51 issandwiched between the transparent electrode 52 and the pixel electrode50. The photodetector 10 also includes an insulating layer 119 formed onat least a portion of the top surface of the transparent electrode 52.The photodetector 10 may further include a protective film 120. Thestructure of the photoelectric conversion film 51 will be described indetail below. The pixel electrode 50 is provided in the interlayerinsulating layer 43C.

The transparent electrode 52 is formed of a semiconductor that istransparent to light to be detected and has conductivity. For example,the transparent electrode 52 is formed of indium tin oxide (ITO),aluminum-doped zinc oxide (AZO), or gallium-doped zinc oxide (GZO), orthe like. The transparent electrode 52 may also be formed of anothertransparent conductive semiconductor. The pixel electrode 50 is formedof, for example, a metal such as aluminum or copper, or a polysilicondoped with impurities and having conductivity.

As illustrated in FIG. 2, the unit pixel cell 14 has a color filter 53above the transparent electrode 52 of the photodetector 10. The unitpixel cell 14 may further include a microlens 54 on the color filter 53.

In the present embodiment, the photoelectric conversion film 51 and thetransparent electrode 52 of each unit pixel cell 14 are connected to thephotoelectric conversion films 51 and the transparent electrodes 52 ofthe adjacent unit pixel cells 14, respectively, and the photoelectricconversion films 51 and the transparent electrodes 52 are formed in anintegrated manner. Note that the photoelectric conversion films 51 maybe separated from each other for each unit pixel cell 14. Moreover, forthe transparent electrodes 52 of the two dimensionally arranged unitpixel cells 14, the transparent electrodes 52 may be connected in anintegrated manner on a row-by-rove basis or a column-by-column basis. Incontrast to this, the pixel electrode 50 of each unit pixel cell 14 isnot connected to the pixel electrodes 50 of the adjacent unit pixelcells 14 and is independently provided.

Note that the image sensor 101 may detect a change in the capacitance ofthe photoelectric conversion film without detecting a charge generatedby photoelectric conversion. Such type of image sensor and imagingdevice are disclosed in, for example, International Publication No.WO2017/081847. That is, the photoelectric conversion film 51 maygenerate electron-hole pairs in relation to the intensity of incidentlight or the capacitance thereof may change in accordance with theintensity of incident light. It is possible to detect light incident onthe photoelectric conversion film 51 by detecting a generated charge ora change in the capacitance.

Configuration of Image Sensor

FIG. 3A is a schematic cross section of the image sensor 101, and FIG.3B is a schematic top view of the image sensor 101 from which theprotective film 120 is removed. In the subsequent figures, thesemiconductor substrate 31 and the interlayer insulating layers 43A,43B, and 43C illustrated in FIG. 2 are collectively illustrated as asubstrate 100.

The image sensor 101 includes the plurality of pixel electrodes 50, thephotoelectric conversion film 51, and the transparent electrode 52,which are described above. The image sensor 101 further includes controlelectrodes 112 and connectors 115, The plurality of pixel electrodes 50and the control electrodes 112 form a circuit portion formed in thesubstrate 100. In addition, the connectors 115 form a portion of thecounter electrode signal lines 16.

The plurality of pixel electrodes 50 are arranged one-dimensionally ortwo-dimensionally and embedded in the substrate 100 so as to leave thetop surface of each of the plurality of pixel electrodes 50 exposed froma top surface 100 a of the substrate 100. The photoelectric conversionfilm 51 is arranged on the top surface 100 a of the substrate 100 so asto cover the plurality of pixel electrodes 50. Furthermore, thetransparent electrode 52 is arranged on the photoelectric conversionfilm 51. The transparent electrode 52 covers a top surface 51 a of thephotoelectric conversion film 51 so as to cover at least the region ofthe photoelectric conversion film 51 where the pixel electrodes 50 areprovided. In the present embodiment, the transparent electrode 52 isformed so as to cover the entire top surface 51 a of the photoelectricconversion film 51.

The insulating layer 119 is formed so as to cover at least a portion ofa top surface 52 a of the transparent electrode 52. The insulating layer119 may cover the top surface 52 a so as to cover at least the region ofthe transparent electrode 52 under which the pixel electrodes 50 areprovided.

Each connector 115 is joined to the corresponding control electrode 112and the transparent electrode 52 and electrically connects theseelectrodes to each other. Specifically, the connector 115 is joined tothe control electrode 112 exposed from the substrate 100 and to a sidesurface 52 s of the transparent electrode 52. Furthermore, the connector115 covers a side surface 51 s of the photoelectric conversion film 51.In addition, the connector 115 covers a portion of a region of a topsurface 119 a of the insulating layer 119, the region not overlying theregion where the pixel electrodes 50 are provided. The area of thejunction of the connector 115 and the control electrode 112 may belarger than, smaller than, or the same as the area of the junction ofthe connector 115 and the transparent electrode 52.

In the present embodiment, in plan view, the photoelectric conversionfilm 51, the insulating layer 119, and the transparent electrode 52 havea rectangular shape, and among four sides 52 c, 52 d, 52 e, and 52 f ofthe transparent electrode 52, the control electrodes 112 are arrangedclose to the sides 52 e and 52 f. Thus, the image sensor 101 includestwo connectors 115, and the two connectors 115 are each joined to thecorresponding control electrode 112 and the corresponding side surface52 s of the transparent electrode 52 at positions close to the sides 52e and 52 f of the transparent electrode 52 and electrically connect thecontrol electrodes 112 to the transparent electrode 52. In the presentembodiment, at each of the four sides 52 c, 52 d, 52 e, and 52 f of thetransparent electrode 52, a side surface 119 s of the insulating layer119 is flush with the side surface 52 s of the transparent electrode 52.

The protective film 120 covers the connectors 115 and the insulatinglayer 119 and is provided on the top surface 100 a of the substrate 100.

The photoelectric conversion film 51 is formed of, for example, anorganic semiconductor. The photoelectric conversion film 51 may includeone or more organic semiconductor layers. For example, the photoelectricconversion film 51 may include, for example, a carrier transport layerfor transporting electrons or holes, a blocking layer for blockingcarriers, and the like in addition to a photoelectric conversion layerfor generating electron-hole pairs. For these organic semiconductorlayers, an organic p-type semiconductor and an organic n-typesemiconductor, which are known materials, can be used.

The transparent electrode 52 is formed of a material among theabove-described materials. The control electrode 112 is formed of ametal or a metallic compound and has a light-blocking property. Forexample, the control electrode 112 is formed of titanium, titaniumnitride, aluminum, silicon and copper doped aluminum, copper, tungsten,or the like or an alloy of any of these metals. The control electrode112 may be formed by a single layer of a material among theabove-described materials or may have a multilayer structure including aplurality of layers.

The connector 115 is formed of a metal or a metallic compound. Forexample, the connector 115 is formed of titanium, titanium nitride,aluminum, silicon, copper-doped aluminum (AlSiCu), copper, tungsten,gold, silver, nickel, cobalt, or the like or an alloy of any of thesemetals. In addition, similarly to the control electrode 112, theconnector 115 may be a single layer or may be multiple layers.

The insulating layer 119 and the protective film 120 are formed of aninsulative material. For example, the insulating layer 119 is formed ofsilicon oxide, silicon nitride, silicon oxynitride, an organic orinorganic polymer material, or the like. The insulating layer 119 andthe protective film 120 may be transparent to light having a wavelengthto be detected by the image sensor 101.

Image Sensor Fabrication Method

The image sensor 101 can be fabricated by, for example, the followingmethod.

(A) Step for Preparing Circuit Portion

First, as illustrated in FIG. 4A, a circuit portion is prepared.Specifically, the substrate 100 is prepared, which has the plurality ofpixel electrodes 50 and the control electrodes 112 exposed at the topsurface 100 a as described above. More specifically, in the circuitportion, each pixel electrode 50 has a structure illustrated in FIG. 2,and the circuit portion can be fabricated using a known semiconductordevice fabrication method.

(B) Step for Forming Photoelectric Conversion Film

As illustrated in FIG. 43, the photoelectric conversion film 51 isformed on the top surface 100 a of the substrate 100 so as to cover atleast the pixel electrodes 50. The photoelectric conversion film 51 canbe formed by, for example, a spin coating method, an inkjet method, adie coating method, a spray coating method, a vacuum deposition method,or a screen printing method.

(C) Step for Forming Transparent Electrode

As illustrated in FIG. 43, the transparent electrode 52 is formed on thephotoelectric conversion film 51. The transparent electrode 52 is formedon at least the region of the photoelectric conversion film 51 where thepixel electrodes 50 are provided. The transparent electrode 52 may beformed by sputtering.

(D) Step for Forming Insulating Layer

As illustrated in FIG. 43, the insulating layer 119 is formed on thetransparent electrode 52. The insulating layer 119 is formed on at leastthe region of the transparent electrode 52 under which the pixelelectrodes 50 are provided. The insulating layer 119 can be formed by,for example, atomic layer deposition (ALD), chemical vapor deposition(CVD), or sputtering.

(E) Patterning Step

The photoelectric conversion film 51, the transparent electrode 52, andthe insulating layer 119 are patterned by removing each of a portion ofthe photoelectric conversion film 51, a portion of the transparentelectrode 52, and a portion of the insulating layer 119. As illustratedin FIG. 4C, a resist film 400, which is photosensitive, is formed on theinsulating layer 119. The resist film 400 is formed by, for example, aspin coating method. Next, by exposing the resist film 400 using a photomask and by performing development, as illustrated in FIG. 4D, a maskhaving a predetermined pattern is formed of the resist film 400.

Next, the photoelectric conversion film 51, the transparent electrode52, and the insulating layer 119 are etched using the mask formed of theresist film 400. The photoelectric conversion film 51, the transparentelectrode 52, and the insulating layer 119 may be patterned by dryetching.

For the insulating layer 119 and the transparent electrode 52, a gascontaining halogens such as fluorine, chlorine, bromine, and iodine maybe used or a gas containing, an element, at least either fluorine orchlorine may be used. Moreover, as dry etching, reactive ion etching(RIE) may be used, in which a gas is converted into a plasma state byplasma discharge, and chemical species of the plasma state gas reactwith the insulating layer 119 and the transparent electrode 52. Theinsulating layer 119 and the transparent electrode 52 are generallyformed of a material containing nitrogen or silicon, and thus theinsulating layer 119 and the transparent electrode 52 can be efficientlyetched using these gases and the etching method.

In contrast, the photoelectric conversion film 51 may be dry-etchedusing a gas containing oxygen. More specifically, a chamber is filledwith a gas containing oxygen, and the photoelectric conversion film 51may be oxidized by chemical etching using oxidation reaction. Thephotoelectric conversion film 51 is rich in carbon, and thus can beremoved as carbon oxides through oxidation reaction with oxygen gas.

In this manner, by etching the insulating layer 119 and transparentelectrode 52 and the photoelectric conversion film 51 using differentgas species, side etching can be adjusted while suppressing damage dueto, for example, plasma at the time of dry etching. In addition, sincethe top surface 51 a of the photoelectric conversion film 51 is coveredby the insulating layer 119, only the side surfaces 51 s are exposed tothe outside during the fabrication process of the image sensor 101.Therefore, it is possible to suppress contact of the photoelectricconversion film 51 with, for example, oxygen, ozone, and moisture anddeterioration of the photoelectric conversion film 51 during etching andduring other fabrication steps.

By performing the patterning step, as illustrated in FIG. 4E, theportion of the photoelectric conversion film 51, the portion of thetransparent electrode 52, and the portion of the insulating layer 119are each removed, and the photoelectric conversion film 51, thetransparent electrode 52, and the insulating layer 119 can be formedthat have a desired pattern and whose side surfaces 51 s, side surfaces52 s, and side surfaces 119 s are exposed. In a case where the amount ofside etching is small, the side surfaces 119 s of the insulating layer119 are positioned substantially flush with the side surfaces 52 s ofthe transparent electrode 52.

(F) Step for Forming Connection Layer

The connectors 115 are formed each of which connects the correspondingside surface 52 s of the transparent electrode 52 to the correspondingcontrol electrode 112. As illustrated in FIG. 4F, a layer 115E formed ofa metal or a metallic compound is formed entirely on the top surface 100a of the substrate 100 so as to cover the top surface 119 a of theinsulating layer 119, the side surfaces 119 s of the insulating layer119, the side surfaces 52 s of the transparent electrode 52, and theside surfaces 51 s of the photoelectric conversion film 51. The layer115B can be formed by, for example, sputtering or a vacuum depositionmethod. Thereafter, a resist film (not illustrated) is formed so as toexpose at least the region under which the pixel electrodes 50 areprovided. By etching the layer 1153 using the resist film as a mask, asillustrated in FIG. 4G, the connectors 115 are formed that are joined tothe control electrodes 112 on the top surface 100 a of the substrate 100and are joined to the side surfaces 52 s of the transparent electrode52.

(G) Step for Forming Protective Film

In a case where the image sensor 101 is provided with the protectivefilm 120, as illustrated in FIG. 4H, the protective film is formed onthe top surface 100 a of the substrate 100 so as to cover the connectors115 and the insulating layer 119. As a result, the image sensor 101 isfabricated.

Characteristics of Image Sensor

In the image sensor 101, a portion of the voltage application path fromthe control electrode 112 to the photoelectric conversion film 51 doesnot need translucency, and wiring in the portion is formed using theconnectors 115, which have higher conductivity than the transparentelectrode 52, instead of the transparent electrode 52. This makes itpossible to apply the voltage of the control electrode 112 to thephotoelectric conversion film 51 with low resistance via the transparentelectrode 52, and voltage fluctuation at the photoelectric conversionfilm 51 is suppressed. Thus, an image sensor that enables more stableimaging is realized. In addition, such an image sensor is used inimaging devices of mobile devices for which lower power consumption isdesired, and imaging devices can be realized that enable a high-speedelectronic shutter or higher-speed spectral sensitivity characteristicswitching.

Moreover, by using the above-described fabrication process, thephotoelectric conversion film 51 is covered by the insulating layer, andit is possible to suppress damage to the photoelectric conversion film51 during the fabrication process of the image sensor. Since thetransparent electrode 52 is in contact with the connectors 115 at theside surfaces 52 s of the transparent electrode 52, the side surfaces 52s for connection to the connectors 115 are formed by patterning thetransparent electrode 52. Unlike the image sensors disclosed in JapaneseUnexamined Patent Application Publication No, 2014-60315 and U.S. Pat.No. 9,224,789, an additional opening for establishing contact does notneed to be formed in the insulating layer 119. This makes it possible toreduce the number of masks and the number of fabrication steps in thefabrication process of the image sensor 101, thereby reducing thefabrication cost and fabrication time of the image sensor 101,Therefore, according to the present embodiment, it is possible tofabricate the image sensor 101, which is a high-performance imagesensor, at low cost.

Other Embodiment

Various modifications can be made to the image sensor 101 of the presentembodiment.

Various modifications can be made to the arrangement and shape of theconnectors 115. As illustrated in FIG. 5, in plan view, a portion 115Aof a connector 115 that covers the top surface 119 a of the insulatinglayer 119 may overlie at least some of the plurality of pixel electrodes50. The connector 115 serves as a light shielding film, and at all timeslight does not enter the unit pixel cells 14 of the pixel electrodes 50that the portion 115A of the connector 115 overlies. Thus, the unitpixel cells 14 can be used to obtain Optical Black, which is a referencesignal for the dark state.

As illustrated in FIG. 6, a connector 115 may be arranged on three sidesof the rectangular shape of the transparent electrode 52. In this case,the connector 115 is joined to the three side surfaces 52 s of the sides52 c, 52 d, and 52 f. In this embodiment, one control electrode 112 isarranged in the top surface 100 a of the substrate 100. According tothis embodiment, although the control electrode 112 is arranged at onlyone position, the connector 115 with low resistance is connected to thethree sides of the transparent electrode 52. The area of the junction ofthe connector 115 and the transparent electrode 52 is increased, andthus the connector 115 and the transparent electrode 52 can beelectrically connected to each other with lower resistance. Therefore, adelay occurring when a voltage is applied to the transparent electrode52 is suppressed, and the isochronous level of voltage changesincreases.

As illustrated in FIGS. 7 and 8, a connector 115 may be arranged on thefour sides of the rectangular shape of the transparent electrode 52. Inthis case, the connector 115 is joined to the four side surfaces 52 s ofthe sides 52 c, 52 d, 52 e, and 52 f. In this case, the connector 115may be provided with a gap 300 as illustrated in FIG. 7 or does not haveto be provided with the gap 300 as illustrated in FIG. 8. In a casewhere the gap 300 is provided as illustrated in FIG. 7, for example,when the connector 115 is formed using a shadow mask, the gap 300 can beused to hold a mask for the opening of a light irradiation region. In acase where the connector 115 is continuously connected to the sidesurfaces 52 s of the four sides of the rectangular shape as illustratedin FIG. 8, a delay occurring when a voltage is applied to thetransparent electrode 52 is more greatly suppressed, and the isochronouslevel of voltage changes increases. Moreover, since the connector 115covers all the side surfaces of the transparent electrode 52 and thephotoelectric conversion film 51, the connector 115 also serves toprevent the photoelectric conversion film 51 from peeling off thesubstrate and serves to prevent the side surfaces of the photoelectricconversion film 51 from being exposed to the atmosphere or the like.

As illustrated in FIGS. 9A and 9B, a portion of the top surface 52 a ofthe transparent electrode 52 does not have to be covered by theinsulating layer 119. Specifically, an outer peripheral portion 52 ap ofthe top surface 52 a is not covered by the insulating layer 119 andexposed from the insulating layer 119. Such a structure can be formedby, for example, etching the insulating layer 119 also in the directionperpendicular to the thickness direction when, as illustrated in FIG.10, the insulating layer 119, the transparent electrode 52, and thephotoelectric conversion film 51 are formed by etching using the resistfilm 400 in the patterning step (E). During the patterning step (E), theinsulating layer 119 is exposed to the etching environment for thelongest period of time, and thus the insulating layer 119 is mostgreatly etched in the direction perpendicular to the thicknessdirection, so that the side surfaces 119 s are recessed and the outerperipheral portion 52 ap of the transparent electrode 52 is exposed. Inthis case, at each of the four sides 52 c, 52 d, 52 e, and 52 f of thetransparent electrode 52, the side surface 119 s of the insulating layer119 is positioned closer to the center of the transparent electrode 52than the side surface 52 s of the transparent electrode 52 is. In thecross section illustrated in FIG. 9B, the ends of the insulating layer119 are positioned toward the inside of the transparent electrode 52relative to the ends of the transparent electrode 52.

The outer peripheral portion 52 ap of the top surface 52 a of thetransparent electrode 52, which is not covered by the insulating layer119, may be covered by and joined to connectors 115. In this case, theconnectors may further cover the protective film 120. Although theconnectors cover the outer peripheral portion 52 ap of the transparentelectrode 52 but the protective film 120 does not have to cover theouter peripheral portion 52 ap. By joining the outer peripheral portion52 ap to the connectors 115, the contact area of the transparentelectrode 52 and the connectors 115 can be further increased, and thetransparent electrode 52 can be electrically connected to the connectors115 with lower resistance.

What is claimed is:
 1. An image sensor comprising: pixel electrodes; acontrol electrode; a photoelectric conversion film arranged on the pixelelectrodes; a transparent electrode arranged on the photoelectricconversion film; an insulating layer arranged on at least a portion of atop surface of the transparent electrode; and a connection layer thatelectrically connects the control electrode to the transparentelectrode, wherein the connection layer is in contact with at least oneside surface of the transparent electrode, and a side surface of theinsulating layer, the at least one side surface of the transparentelectrode, and a side surface of the photoelectric conversion film arealigned with each other.
 2. The image sensor according to claim 1,wherein the connection layer is further in contact with the side surfaceof the photoelectric conversion film.
 3. The image sensor according toclaim 1, wherein the connection layer covers a portion of the insulatinglayer.
 4. The image sensor according to claim 1, wherein the connectionlayer is not in contact with the top surface of the transparentelectrode.
 5. The image sensor according to claim 1, wherein, in planview, the connection layer partially overlaps with the pixel electrodes.6. The image sensor according to claim 1, wherein the connection layerhas a light-blocking property.
 7. The image sensor according to claim 1,further comprising: a protective film that covers the connection layerand the insulating layer.
 8. The image sensor according to claim 1,wherein in plan view, the transparent electrode has a polygonal shape,the at least one side surface of the transparent electrode includes aplurality of side surfaces, and the connection layer is in contact withthe plurality of side surfaces of the transparent electrode.
 9. Theimage sensor according to claim 1, wherein a hole through which the topsurface of the transparent electrode is connected to the connectionlayer is not arranged in the insulating layer.
 10. The image sensoraccording to claim 1, wherein, in plan view, the connection layeroverlaps with at least a portion of the insulating layer, at least aportion of the transparent electrode, and at least a portion of thephotoelectric conversion film.
 11. A method for fabricating an imagesensor, the method comprising: preparing a substrate on which pixelelectrodes and a control electrode are provided; forming a photoelectricconversion film on the pixel electrodes; forming a transparent electrodeon a top surface of the photoelectric conversion film; forming aninsulating layer on the transparent electrode; patterning thephotoelectric conversion film, the transparent electrode, and theinsulating layer so that a side surface of the insulating layer, a sidesurface of the transparent electrode, and a side surface of thephotoelectric conversion film are aligned with each other; and forming aconnection layer that electrically connects the side surface of thetransparent electrode, which is exposed by the patterning, to thecontrol electrode.
 12. The method according to claim 11, wherein, in thepatterning, a hole through which a top surface of the transparentelectrode is connected to the connection layer is not formed in theinsulating layer.
 13. The method according to claim 11, wherein, in theforming of the connection layer, the connection layer is brought intocontact with the photoelectric conversion film.
 14. The method accordingto claim 11, wherein in the patterning, the insulating layer ispatterned so as to expose an outer periphery of a top surface of thetransparent electrode, and in the forming of the connection layer, theconnection layer is brought into contact with the outer periphery of thetransparent electrode.
 15. The method according to claim 11, wherein, inthe forming of the connection layer, the connection layer is formed onat least a portion of the insulating layer.